Deep Vein Thrombosis (DVT)

Summary for patients:

Deep Vein Thrombosis (DVT)  is when a blood clot occurs in the deep veins of the leg causing pain and swelling. If any part of the clot breaks off and travels to the lungs, it can cause a potentially fatal condition called a Pulmonary Embolism. There are many reasons it can occur but as one of the risk factors is inactivity, regular exercise can help. You can also help prevent DVT by wearing compression stockings, as they help maintain the speed of blood flow through the legs.

For health practitioners:

Deep Venous Thrombosis (DVT) is the clinical term used for the formation of a blood clot (thrombus) in the deep veins of the leg. If the thrombus or any part of it breaks off and travels in the blood, this is known as an embolism and if it travels to the lungs (Pulmonary Embolism) it is potentially fatal.1

The term Venous Thromboembolism (VTE) is used to encompass the conditions of Deep Venous Thrombosis and Pulmonary Embolism. An estimated 25,000 people die from this hospital acquired condition every year (More than Breast Cancer, Road Traffic Accidents and AIDS added together).2

Signs and symptoms

Approximately 50% of DVT’s are asymptomatic and 4 out of 5 go undetected as their symptoms mimic other conditions.3 However, the most common signs are: swelling in the calf; pain and tenderness in the leg; red discoloured skin, increased warmth to the calf and engorged collateral veins.

Symptomatic DVT can lead to Chronic Venous Insufficiency, venous ulceration and the development of Post-thrombotic limb.


Rudolph Virchow explained that it was the coming together of 3 predisposing factors which lead to the formation of a DVT: Decreased blood flow (venous stasis), Coagulation changes (hypercoagulability) and changes to the lining of the vessel wall. This is now known as Virchow’s Triad4 and the interaction of these factors occur during surgery increasing the risk of developing a DVT. Orthopaedic surgery carries the highest risk due to long-term venous stasis during the operation.

Several factors can also increase the risk of DVT, the most common being immobility. Other risk factors include obesity (BMI > 30), old age, cancer and related therapies, the contraceptive pill and HRT, trauma, varicose veins and multiple co-morbidities.5

Diagnosis is usually through the D-Dimer test which detects fragments of broken down clots or Duplex Doppler ultrasound which shows the blood-flow in the legs.

Prophylaxis and Prevention

Sub-cutaneous Low Molecular Weight Heparin (LMWH), intermittent pneumatic compression and anti-embolism stockings are all used to reduce the risk of developing a DVT, dependent on local protocol, patient condition and patient preference. LMWH reduces the clotting ability of the blood, whilst the pneumatic compression and stockings, maintain the speed of blood flow through the legs, reducing the risk of stasis.

  1. NICE Clinical Guideline 92 (January 2010)
  2. House of Commons Health Committee 2005
  3. Sandler DA, Martin JF (1989) Autopsy proven pulmonary embolism in hospitalised patients. Journal of Royal Society of Medicine. 82:203-205
  4. Virchow 1856
  5. Lijfering WM, Rosendaal FR, Cannegieter SC (2010). “Risk factors for venous thrombosis – current understanding from an epidemiological point of view”. Br J Haematol 149 (6): 824–33